Biaxially oriented sealable polypropylene film having improved barrier properties

ABSTRACT

A sealable film is disclosed comprising (i) a base layer comprising polypropylene and a hydrocarbon resin and (ii) at least one top layer comprising (a) an ethylene/propylene copolymer having an ethylene content of not more than about 10% by weight, (b) a propylene/1-butene copolymer, (c) a propylene/ethylene/alpha-olefin terpolymer, or (d) a blend of two or more of (a), (b) and (c), wherein at least one of said base layer and said at least one top layer contains an anti-blocking agent or lubricant. The film possesses improved barrier properties with respect to permeability to water vapor and oxygen, and which at the same time exhibits favorable slip properties and low shrink values.

BACKGROUND OF THE INVENTION

This application is a continuation-in-part of U.S. Ser. No. 07/734,157,filed Jul. 22, 1991 now abandoned. U.S. Ser. No. 07/734,157 is herebyincorporated by reference in its entirety.

The present invention relates to a multilayer polypropylene film whichhas been produced by coextrusion and which has improved barrierproperties with respect to permeability to water vapor and oxygen andsimultaneously possesses favorable slip properties and low shrinkvalues, in order to ensure good machine running properties.

EP-A-0,247,898 (=U.S. Pat. No. 4,921,749) describes a specialpolypropylene film which is claimed to possess, in particular,high-strength sealed seams and improved barrier properties.

DE-A-35 35 472 (=U.S. Pat. No. 4,786,533) is directed to polypropylenefilms where a certain amount of resin is incorporated in the base layer.However the films disclosed therein possess, in particular, inadequatebarrier properties towards water vapor, so that there has been a needfor films having improved properties in this respect.

DE-A-38 14 942 describes polypropylene films containing a resinproportion of 5 to 40% by weight in their base layers, the resins havinga softening point in the range of 80° to 125° C. These films are used asshrink-on labels, but exhibit disadvantages with respect to the barrierproperties towards water vapor and oxygen.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide apolypropylene film having improved barrier properties with respect topermeability to water vapor and oxygen, while at the same time havingfavorable slip properties and low shrink values.

Another object of the present invention is to provide a process forproducing the improved film.

In accomplishing the foregoing objectives, there has been provided, inaccordance with one aspect of the present invention, a sealable filmcomprising (i) a base layer comprising polypropylene and a hydrocarbonresin having a softening point of at least 140° C. and (ii) at least onetop layer comprising (a) an ethylene/propylene copolymer having anethylene content of not more than about 10% by weight, (b) apropylene/1-butene copolymer, (c) a propylene/ethylene/alpha-olefinterpolymer, or (d) a blend of two or more of (a), (b) and (c), whereinsaid top layer contains an anti-blocking agent.

In another embodiment of the invention, the hydrocarbon resins has asoftening point of less than 140° C., preferably from about 100° to 138°C.

In accordance with another aspect of the present invention there isprovided a process for producing the foregoing film comprising the stepsof: producing by coextrusion through a slot die a cast film comprisingsaid base layer and at least one said top layer; chilling said cast filmon a chill roll; and then orienting said film by biaxial stretching inthe longitudinal and transverse directions.

In accordance with still another aspect of the present invention thereis provided a process for producing a multilayer sealable filmcomprising the step of incorporating in at least one layer of said filma resin having a softening point of at least 140° C. or less than 140°C.

Other objects, features and advantages of the present invention willbecome apparent to those skilled in the art from the following detaileddescription. It is to be understood, however, that the detaileddescription and specific examples, while indicating preferredembodiments of the present invention, are given by way of illustrationand not limitation. Many changes and modifications within the scope ofthe present invention may be made without departing from the spiritthereof, and the invention includes all such modifications.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In comparison to the films according to DE-A-38 14 942, the filmsaccording to the present invention display reduced deposits on therollers.

Compared to the film disclosed in that publication, the film of theinstant invention is distinguished by improved processability, inparticular with respect to machine running properties on high-speedpackaging machines and to thermal blocking. The term "machine runningproperties" refers to the ease of processing on high-speed packagingmachines. For this purpose, the film must be neither too smooth nor toorough, for this might cause jams during the slitting operation. Thestiffness of a film is also important in this respect. The term "thermalblocking" relates to the mutual adhesion of film-packaged goods, whichis, above all, caused by the action of heat. The lower this mutualadhesion between two adjoining film layers under the action of heat is,the better is the thermal blocking behavior.

In comparison to the films according to DE-A-38 14 942, the filmsaccording to the present invention display reduced deposits on therollers.

The terpolymer described under (c) above is preferably comprised ofabout 93.2 to 99.0% by weight of propylene, about 0.5 to 1.9% by weightof ethylene and about 0.5 to 4.9% by weight of the alpha-olefin, thepercentages relating to the total weight of the terpolymer.

The base layer of the multilayer film is comprised of a propylenepolymer having a melting point in the range of about 162° to 168° C.Isotactic polypropylene having an n-heptane-soluble fraction of 6% orless is preferably used. The polypropylene of the base layer in generalhas a melt flow index of about 1.5 to 5 g/10 min, measured under a loadof 21.6N and at a temperature of 230° C., according to DlN 53 735.

The base layer preferably has a modulus of elasticity in thelongitudinal direction of less than 3000 N/mm², more preferably lessthan 2800 N/mm², most preferably 2200 to 2800 N/mm². The modulus ofelasticity in the transverse direction is preferably less than 5200N/mm², more preferably in the range from 4000 to 5100 N/mm². The modulusof elasticity is determined according to DIN 53,457 or ASTM-D 882,respectively.

The low-molecular weight resin contained in the base layer is a naturalor synthetic resin having a softening point of ≧140° C. or a softeningpoint of <140° C., such as from 100° to 138° C., determined according toDIN 1995-U4, corresponding to ASTM E-28, and it is present in an amountof about 5 to 30% by weight, preferably of about 5 to 20% by weight,most preferably 5 to 10% by weight, relative to the total weight of thebase layer. Surprisingly, it was found that as a result of incorporatinga resin having a softening point in the range specified above into thepolypropylene, the barrier properties of the films towards water vaporare substantially improved, and that at the same time the opticalproperties and also the shrink behavior of the film are favorablyinfluenced. Moreover, the films according to this invention do not leadto deposits on rollers, e.g., during the longitudinal stretching. It hasalso been shown that as a result of their particular slip properties,the films of this invention are especially well-suited for use onhigh-speed packaging machines. The film surface is smooth enough toavoid so-called `slip-stick` effects, i.e., irregular running speeds. Onthe other hand, the roughness of the film surface is sufficiently highto avoid jams prior to the actual slitting operation.

From among the numerous low-molecular weight resins, preference is givento the hydrocarbon resins, in particular to the petroleum resins,styrene resins, cyclopentadiene resins and terpene resins (these resinsare described in detail in `Ullmanns Enzyklopadie der TechnischenChemie` (Ullmann's Encyclopedia of Technical Chemistry), 4th edition,vol. 2, pp. 539-553). The term `petroleum resins` defines hydrocarbonresins produced by polymerization of deep-decomposed petroleumcomponents in the presence of a catalyst. These petroleum materialsusually contain a mixture of resin-forming substances, such as styrene,methylstyrene, vinyltoluene, indene, methylindene, butadiene, isoprene,piperylene and pentylene. The styrene resins are low-molecular weightstyrene homopolymers or copolymers of styrene and other monomers, suchas alpha-methylstyrene, vinyltoluene and butadiene. The cyclopentadieneresins are cyclopentadiene homopolymers or cyclopentadiene copolymersobtained from coal tar distillates and fractionated petroleum gas. Theresins are produced by subjecting the cyclopentadiene-containingmaterials to high temperatures over a prolonged period of time.Depending on the reaction temperature, dimers, trimers or oligomers areobtained.

The terpene resins include polymers of terpenes, i.e., hydrocarbons ofthe formula C₁₀ H₁₆, which are present in practically all etherial oilsor oil-containing vegetal resins, and also phenol-modified terpeneresins. Specific examples of suitable terpenes include alpha-pinene,beta-pinene, dipentene, limonene, myrcene, camphene and similarterpenes. The hydrocarbon resins may also be chosen from among theso-called modified hydrocarbon resins. Modification is generallyperformed by reacting the raw materials prior to polymerization, byintroducing special monomers or by reacting the polymerized product,whereby preference is given to hydrogenations or partial hydrogenations.

Suitable hydrocarbon resins also include styrene homopolymers, styrenecopolymers, cyclopentadiene homopolymers, cyclopentadiene copolymersand/or terpene polymers, which in each case have a softening point of≧140° C. (among the unsaturated polymers, preference is given to thehydrogenated products). Particularly preferably, the cyclopentadienehomopolymers having a softening point of ≧140° C. are employed in thebase layer.

If the top layer(s), too, are to contain a hydrocarbon resin, the resinslisted above in the listed amounts for the base layer can be used. Inthis case, it is, also possible to employ hydrocarbon resins having asoftening point of ≧140° C. such as between 100° C. and 183° C.

In order to further improve certain properties of the film according tothis invention, effective amounts of suitable additives may beincorporated both in the base layer and in the top layer(s). Preferredadditives include antistatic agents and/or antioxidants.

Straight-chain and saturated, aliphatic, tertiary amines, which possessa C₁₀ to C₂₀ aliphatic radical and two 2-hydroxy-(C₂ -C₄)alkyl groupsare preferred antioxidants. N-(C₁₀ -C₂₀)-, and especially N-(C₁₂-C₁₈)alkyl-N',N"-bis-(2-hydroxyethyl)-amines are employed particularlypreferably.

The antioxidants employed preferably are so-called primary antioxidants,i.e., sterically hindered phenols or secondary amines, but it is alsopossible to use secondary antioxidants, such as, for example, thioethersor phosphites or phosphonites, or synergistic mixtures of primary andsecondary anitoxidants. Antioxidants of this generic type are described,for example, in Gachter/Muller: Kunststoff-Additive (PlasticsAdditives), Carl Hanser Verlag, 2nd edition (1983). Below, thestructural formulae of a number of suitable compounds are given:##STR1##

Preferred lubricants include carboxylic acid amides, such as erucic acidamide and stearic acid amide, or polydiorganylsiloxanes.

Suitable anti-blocking agents include, for example, organic polymerswhich are incompatible with the raw material employed for the toplayer(s), such as polyamides, polyesters, polycarbonates and the like,or inorganic substances such as silicates, silicon dioxide and calciumcarbonate. Inorganic substances, in particular silicon dioxide, with anaverage particle size of 1 to 6 μm, have found to be most suitable.These anti-blocking agents are added in amounts of about 0.1 to 1% byweight, preferably of about 0.15 to 0.5% by weight, relative to theweight of the top layer(s).

The thickness of the top layer(s) preferably varies between about 0.4and 1.0 μm.

The parameters for producing the films according to this invention areexpediently selected such that stretching in the longitudinal directionis performed at a temperature between about 100° and 130° C., preferablybetween about 105° and 120° C., and at a stretch ratio between about 1:4and 1:6. Stretching in the transverse direction is performed at atemperature between about 120° and 160° C., preferably between about130° and 150° C. The stretching ratio in the transverse direction ishigher than about 1:7.5, and preferably it is in the range of about 1:8to 1:11. Following the stretching state in the transverse direction, thefilm is heat-set. During this treatment the film is conveyed in thetenter frame, optionally in a slightly converging manner, at atemperature which is about 5° to 50° C. below the stretchingtemperature. Preferably, a convergence range of about 5 to 15% is setfor the heat-setting treatment. Ready printability of the film isachieved by subjecting the film to one of the conventional treatmentsprior to winding, such as, for example, to a flame treatment orelectrical corona treatment. Corona treatment by means of any of theknown methods is expediently performed such that the film is passedbetween two conductor elements which serve as electrodes, whereby avoltage which is high enough to cause spray or corona discharges isapplied between the electrodes. This usually is an alternating voltageof about 10,000 V and a frequency of about 10,000 Hz. As a result ofthese spray or corona discharges, the air above the film is ionized andreacts with the molecules of the film surface, so that polar inclusionsare obtained in the essentially non-polar polymer matrix. The treatmentintensities are within the usual range; preferably they are between 38and 42 mN/m.

The invention will be illustrated in greater detail by way of theExamples which follow. A comparative survey is given in Table 1.

EXAMPLE 1

A three-layered, transparent film having a total thickness of 20 μm wasproduced by coextrusion and subsequent orientation by biaxialstretching. The film had the layer build-up ABA, `A` denoting the toplayers and `B` denoting the base layer. Each of the top layers was 0.6μm thick.

The base layer was comprised of polypropylene to which 10% by weight ofresin (ESCOREZ® ECR 356, supplied by Exxon, Darien, Conn., USA;softening point of the resin: 140° C.), relative to the total weight ofthe blend, had been added. The polypropylene had a melt flow viscosityof 3.5 g/10 min, determined according to DIN 53 735, under a load of2.16 kg.

The top layers were comprised of a propylene/ethylene copolymer havingan ethylene content of 4.8% by weight, to which 0.8% by weight ofpolydimethylsiloxane, 0.13% by weight of a phenolic stabilizer(Antioxidant 330, supplied by Ethyl Corp., Brussels, Belgium, and BatonRouge, La., USA), 0.075% by weight of calcium stearate and 0.33% byweight of SiO₂ having an average particle size of 2 μm, had been added.The polydimethylsiloxane had a kinematic viscosity of 30,000 mm² /sec;the propylene/ethylene copolymer had a melt flow viscosity of 6.0 g/10min, measured according to DIN 53 735, under a load of 2.16 kg.

EXAMPLE 2

A film was produced as described in Example 1, except that the resincontent of the base layer was 20% by weight (same resin as in Example1).

EXAMPLE 3

A film was produced as described in Example 1, except that the resincontent of the base layer was 30% by weight (same resin as in Example1).

EXAMPLE 4

A film was produced as described in Example 2, except that the layerbuild-up was ABC. Top layer `A` had been corona-treated and did notcontain any polydimethylsiloxane, whereas in top layer `C` thepolydimethylsiloxane content had been doubled. Layer B was the baselayer.

EXAMPLE 5

A film was produced as described in Example 2, except that the layerbuild-up was ABC. Top layer `C` was comprised of a blend comprising anethylene/propylene copolymer with an addition of 10% by weight of theresin employed in Example 1.

EXAMPLE 6

A film was produced as described in Example 1 except that the resin wasREGALITE® R101 (Hercules) having a softening point of 100° C.

EXAMPLE 7

A film was produced as described in Example 1 except that the resin wasREGALREZ® 1128 (Hercules) having a softening point of 130° C.

COMPARATIVE EXAMPLE 1 (C1)

A film was produced as described in Example 1, but without the additionof the resin.

COMPARATIVE EXAMPLE 2 (C2)

A film was produced as described in Example 1, except that a resinhaving a softening point of 85 ° C. was employed (ESCOREZ® 5380,supplied by Exxon).

COMPARATIVE EXAMPLE 3 (C3)

A film was produced as described in Example 2, except that no SiO₂ wascontained in the top layers.

In Table 1 below, the properties of the films described in the Examplesand Comparative Examples are expressed in numerical values or rated asfollows:

++=very good or no resin deposition on the rollers

+=good or hardly any resin deposition on the rollers

-=poor or noticeable resin deposition on the rollers

--=unacceptable or severe resin deposition on the rollers

Determination of Thermal Blocking

To determine the thermal blocking properties, two wooden blocks (72mm×41 mm×13 mm), to one surface of which a piece of felt had been glued,are wrapped into a sample of the film to be tested and sealed. The twoblocks are stacked on top of one another, with the felt-clad surfacesfacing each other, and loaded with a weight of 200 g. This arrangementis put in an oven preheated to 70° C. and left there for two hours. Thenthe temperature is reduced to room temperature (21° C.) for 30 minutesand the weight is lifted off from the wooden blocks. By means of amechanical appliance the upper block is removed from the lower block.Evaluation is performed over the course of 4 individual measurements,from which the maximum take-down force (measured in N) is determined.

The requirements of the specification are fulfilled if none of theindividual measurements exceeds 5N.

Determination of Haze

The haze of the film is determined by a method similar to ASTM-D1003-52, whereby a 1° slot aperture is used instead of the 4° roundaperture, and the haze is indicated for four superimposed films, becausein this way measurement can be performed within the optimum range. Hazeis evaluated as follows:

up to 15%: very good

15 to 25%: moderate

over 25%: unsatisfactory

Determination of Gloss

The gloss of the films is determined according to DIN 67 530. Thereflector value is measured as an optical quantity for the surface of afilm. In accordance with the ASTM-D 523-78 and ISO 2813 standards, theangle of radiation incidence is adjusted to 20°. A light beam hits theplanar test surface at the set angle of incidence and is reflected orscattered by the test surface. The light beams incident on thephotoelectronic receiver are indicated as a proportional electricalquantity. The measured value is dimensionless and must be given with theangle of incidence. The gloss (angle of incidence 20°) is evaluatedusing the following ratings:

down to 115: very good

115 to 100: moderate, and

less than 100: poor

Determination of Modulus of Elasticity

The modulus of elasticity is determined according to DIN 53,457 orASTM-D 882.

Determination of Shrink

The shrink of a film is defined as the percental change in length (l_(o)-l/l_(o)). Square film samples having a side length of 10 cm (l_(o)) areheated to a temperature of 120° C. for five minutes. Then the remaininglength (1) is measured.

Determination of Permeability to Water Vapor and Oxygen

The permeability to water vapor is determined in accordance with DIN 53122, part 2.

The barrier effect towards oxygen is measured according to draftstandard DlN 53 380, part 3, at an atmospheric moisture content of 53%.

The Table shows that with regard to the desired combination ofproperties, the films according to the present invention are superior tothe films according to the Comparative Examples.

                                      TABLE 1                                     __________________________________________________________________________                          Shrink 120° C.                                                O.sub.2 -Perm.                                                                         5 min in %           Optical                                 WVP (g/m.sup.2 · d)                                                          (cm.sup.3 /m.sup.2 · d · bar)                                        longit./                                                                              Friction                                                                            Thermal                                                                              Properties                                                                          Resin Depos.                                                                         Machine               Example                                                                            in %    in %     transv. DIN 53375                                                                           Blocking (N)                                                                         Haze/Gloss                                                                          on Rollers                                                                           Runnability           __________________________________________________________________________    1    0.88    1080     5/2     0.35  1      19/130                                                                              +      ++                    2    0.79     770     7/3     0.35  1      18/125                                                                              +      ++                    3    0.66     750     10/3    0.35  1      15/130                                                                              +      ++                    4    0.79     770     7/3     0.35  1      19/125                                                                              +      ++                    5    0.70     760     7/3     0.35  0.8    17/130                                                                              +      ++                    6    0.93    1050     7/2     0.35  1      17/125                                                                              +      ++                    7    0.95    1100     6/3     0.35  1      18/128                                                                              +      ++                    C1   1.40    1800     3/1     0.35  1      25/115                                                                              ++     ++                    C2   0.85    1200     10/5    0.35  1      21/120                                                                              -      ++                    C3   0.79    1150     7/3     0.45  5      20/130                                                                              ++     -                     __________________________________________________________________________     WVP: Permeability to water vapor                                              O.sub.2Perm.: Permeability to oxygen                                          Friction: Determined according to DIN 53 375                                  Resin deposition on the rollers and machine runnability were evaluated by     subjective visual inspection.                                            

What is claimed is:
 1. A sealable film comprisingi) a base layercomprising polypropylene and a hydrocarbon resin having a softeningpoint of at least 140° C., and ii) a top layer comprisinga) anethylene/propylene copolymer having an ethylene content of not more thanabout 10% by weight, or b) a propylene/1-butene copolymer, or c) apropylene/ethylene/alpha-olefin terpolymer, or d) a blend of two or moreof a), b) and c), wherein said top layer contains an anti-blocking agentwith an average particle size of 1 to 6 μm and wherein the top layer hasa thickness of about 0.4 to about 1.0 μm.
 2. A sealable film as claimedin claim 1, wherein said ii ) comprises a propylene/1-butene copolymerb) which has a 1-butene content of about 10 to 15% by weight.
 3. Asealable film as claimed in claim 1, wherein ii) comprises c) and saidalpha-olefin is an alpha-olefin having 4 to 10 carbon atoms.
 4. Asealable film as claimed in claim 1, wherein ii) comprises c) and saidalpha-olefin is selected from the group consisting of 1-butene,1-pentene and 1-hexene.
 5. A sealable film as claimed in claim 1,wherein ii) comprises a terpolymer c) which comprises about 93.2 to99.0% by weight of propylene, about 0.5 to 1.9% by weight of ethyleneand about 0.5 to 4.9% by weight of alpha-olefin.
 6. A sealable film asclaimed in claim 1, wherein said hydrocarbon resin is contained in saidbase layer in an amount of about 5 to 30% by weight.
 7. A sealable filmas claimed in claim 6, wherein said hydrocarbon resin is contained insaid base layer in an amount of about 10 to 20% by weight.
 8. A sealablefilm as claimed in claim 1, wherein said hydrocarbon resin of said baselayer is selected from the group consisting of petroleum resins, styreneresins, cyclopentadiene resins and terpene resins.
 9. A sealable film asclaimed in claim 8, wherein said hydrocarbon resin is a cyclopentadieneresin.
 10. A sealable film as claimed in claim 1, wherein at least oneof said base layer and said top layer contains an antistatic agent or anantioxidant.
 11. A sealable film as claimed in claim 10, wherein saidfilm contains an antioxidant which is a primary or secondaryantioxidant.
 12. A sealable film as claimed in claim 1, wherein saidantiblocking agent is selected from the group consisting of silicates,SiO₂ and calcium carbonate.
 13. A sealable film as claimed in claim 1,which contains a lubricant which is a carboxylic acid amide or apolydiorganylsiloxane.
 14. A sealable film as claimed in claim 1,wherein said film is comprised of one base layer and two top layers. 15.A sealable film as claimed in claim 14, wherein each side of said baselayer is covered by a top layer.
 16. A packaging material comprising asealable film as claimed in claim
 1. 17. A sealable film as claimed inclaim 1, wherein said base layer has a modulus of elasticity in thelongitudinal direction of less than 3000 N/mm² and a modulus ofelasticity in the transverse direction of less than 5200 N/mm².
 18. Asealable film as claimed in claim 17, wherein the modulus of elasticityin the longitudinal direction is less than 2800 N/mm² and in thetransverse direction is in the range from 4000 to 5100 N/mm².
 19. Asealable film comprisingi) a base layer comprising polypropylene and ahydrocarbon resin having a softening point of from about 100° C. to lessthan 140° C., and ii) a top layer comprisinga) an ethylene/propylenecopolymer having an ethylene content of not more than about 10% byweight, or b) a propylene/1-butene copolymer, or c) apropylene/ethylene/alpha-olefin terpolymer, or d) a blend of two or moreof a), b) and c), wherein said top layer contains an anti-blocking agentwith an average particle size of 1 to 6 μm and wherein the top layer hasa thickness of about 0.4 to about 1.0 μm.
 20. A sealable film as claimedin claim 19, wherein the softening point is from about 100° C. to 138°C.
 21. A sealable film as claimed in claim 19, wherein said ii)comprises a propylene/1-butene copolymer b) which has a 1-butene contentof about 10 to 15% by weight.
 22. A sealable film as claimed in claim19, wherein ii) comprises c) and said alpha-olefin is an alpha-olefinhaving 4 to 10 carbon atoms.
 23. A sealable film as claimed in claim 19,wherein ii) comprises c) and said alpha-olefin is selected from thegroup consisting of 1-butene, 1-pentene and 1-hexene.
 24. A sealablefilm as claimed in claim 19, wherein ii) comprises a terpolymer c) whichcomprises about 93.2 to 99.0% by weight of propylene, about 0.5 to 1.9%by weight of ethylene and about 0.5 to 4.9% by weight of alpha-olefin.25. A sealable film as claimed in claim 19, wherein said hydrocarbonresin is contained in said base layer in an amount of about 5 to 30% byweight.
 26. A sealable film as claimed in claim 19, wherein saidhydrocarbon resin is contained in said base layer in an amount of about10 to 20% by weight.
 27. A sealable film as claimed in claim 19, whereinsaid hydrocarbon resin of said base layer is selected from the groupconsisting of petroleum resins, styrene resins, cyclopentadiene resinsand terpene resins.
 28. A sealable film as claimed in claim 19, whereinsaid hydrocarbon resin is a cyclopentadiene resin.
 29. A sealable filmas claimed in claim 19, wherein at least one of said base layer and saidtop layer contains an antistatic agent or an antioxidant.
 30. A sealablefilm as claimed in claim 19, wherein said film contains an antioxidantwhich is a primary or secondary antioxidant.
 31. A sealable film asclaimed in claim 19, wherein said antiblocking agent is selected fromthe group consisting of silicates, SiO₂ and calcium carbonate.
 32. Asealable film as claimed in claim 19, which contains a lubricant whichis a carboxylic acid amide or a polydiorganylsiloxane.
 33. A sealablefilm as claimed in claim 19, wherein said film is comprised of one baselayer and two top layers.
 34. A sealable film as claimed in claim 19,wherein each side of said base layer is covered by a top layer.
 35. Apackaging material comprising a sealable film as claimed in claim 19.36. A sealable film as claimed in claim 19, wherein said base layer hasa modulus of elasticity in the longitudinal direction of less than 3000N/mm² and in the transverse direction of less than 5200 N/mm².
 37. Asealable film as claimed in claim 19, wherein the modulus of elasticityin the longitudinal direction is less than 2500 N/mm² and in thetransverse direction is in the range from 4000 to 5100 N/mm².